With the increased popularity of the Internet has come increasing demand for faster means of accessing the information on the Internet. To meet this demand, broadband technologies such as, for example, the Digital Subscriber Line (DSL), Hybrid Fiber/Coax (HFC) using the cable system, and wireless point-to-point networks are being delivered right to the residential consumer. As the prices associated with the use of such technology have come down, the acceptance of the technology and install rates have soared. An example architecture for a broadband network is provided below, with reference to FIG. 1.
Turning to FIG. 1 an example HFC CATV system is presented, in accordance with one example embodiment. In accordance with the illustrated example embodiment, HFC network 100 is depicted comprising a master headend 102, coupled to a number of primary hubs 104A-N via a communication network 106. Each of the primary hubs 104A-N are coupled to secondary hubs 108A-N and, subsequently, a number of fiber nodes 110A-N in a tree-branch configuration as shown. According to one implementation of the HFC network 100, network 106 includes synchronous optical network (SONET) equipment that communicates over single mode fiber (SMF), and the fiber optic communication path extends to the fiber node(s) 110. Each of the fiber nodes 110 provides cable service to network end-points (e.g., residential drops, commercial drops, etc.) via a broadband coaxial connection 112, using repeater amplifiers 114A-N, as needed.
It will be appreciated by those skilled in the art that in order to use any of the broadband systems introduced above, a broadband modem (modulator/demodulator) is required. In accordance with the illustrated cable television example, a cable modem is required. Cable modems, first developed in the early 90's, enable a computing system to utilize one or more channels of the broadband signal for the interchange of data with, for example, Internet network elements (e.g., web servers, etc.). In this regard, cable modems modulate/demodulate data channels in an unused section of the broadcast bandwidth of the cable television (CATV) system.
FIG. 1 also illustrates a typical residential drop 116 of the HFC network 100 as comprising a splitter 118, which provides a CATV signal to one or more A/V systems 120, as well as to one or more computing systems 124 through a cable modem 122. In accordance with the Data Over Cable Service Interface Specification (DOCSIS 1.1) Radio Frequency Interface Specification SP-RFIv1.1-106-001215 first released Mar. 11, 1999 by the CableLabs® consortium, conventional fiber nodes 110A-N typically broadcast (i.e., forward or downlink component) to network end-points using M-ary quadrature amplitude modulation (QAM) (e.g., 64- or 256 QAM) in 6 MHz channels over a band from 91-857 MHz. In the upstream, (i.e., reverse or uplink component) a cable modem 122 transmits in bursts to the fiber node 110A-N using Reed-Solomon encoding and quadrature phase shift-keying (QPSK) or QAM-16 in one of the following channel widths (−30 dB bandwidth) of 200-kHz, 400-kHz, 800-kHz, 1.6-MHz, and 3.2-MHz from 5 to 42-MHz (5-65-MHz for EuroDOCSIS). Simply stated, QAM is a combination of phase shift-keying and amplitude shift-keying. That is to say, the information to be transmitted in a QPSK signal is modulated in phase shifts, while the information to be transmitted in a QAM signal is modulated in phase and amplitude shifts, i.e., the differences in phase and amplitude.
In accordance with the illustrated example implementation, A/V system(s) 120 are cable ready, i.e., include the necessary tuner and demodulator hardware required to access broadcast programming information contained within the CATV signal. In alternate implementations wherein the AV system does not include the logic to demodulate the QAM digital signal, an additional set-top box (STB) (not shown) is required to demodulate the digital signal to an analog form expected by the tuners of the AV system 120.
Given the dual purpose of data enabled CATV systems, i.e., providing analog and digital programming as well as data channels, the cable modem has certain technical challenges that other broadband modems do not have to deal with. Given the typical implementation of 6 MHz channels over a spectrum of 91-857 MHz, one of the problems cable modems have is identifying which of the over 125 channels in the broadband signal are data channels, and which are allocated to other programming (e.g., A/V) channels. Conventional cable modems use one of a number of “brute force” methods to distinguish data channels from digital multimedia channels. According to one such method, a cable modem simply traverses each of the 130-plus channels, demodulating the content to determine whether the channel is a data channel. This solution is unpopular due to the fact that it is time consuming, often taking over a minute to complete this sweep and distinguish data channel(s) from digital media channels.
Another solution, implemented when the CATV system provider also distributes the cable modems is to group the data channels to a particular sub-band of channels within the CATV band. The cable modems are populated with a bandpass filter designed to constrain the channel sweep described above to the data channel sub-band pre-determined by the CATV operator. This solution has the obvious disadvantage that it fixed in hardware, and for the operator to extend the range of available data channels would require a hardware fix in the cable modems. In this regard, the modems are not readily amenable to upgrade.